Atherosclerotic cardiovascular disease, hyperlipidemias, and obesity are three prevalent diseases where the abnormal accumulation of lipids is known to seriously affect our population largely through heart and vessel disorders. Since the defective regulation of lipid synthesis in animal cells may underlie the molecular basis of these pathologies, investigations on the regulatory mechanisms controlling the synthesis of triacylglycerol, the principal storage fuel of animals, and phospholipids, ubiquitous components of biological membranes and serum lipoproteins, are proposed using isolated rat fat cells and "adipocytes" in culture. The objectives of the proposed investigations are to determine whether several microsomal enzymes (sn-glycerol-3-phosphate acyltransferase, dihydroxyacetonephosphate acyltransferase, 1-acylglycerol-3-phosphate acyltransferase, phosphatidate phosphatase, diacylglycerol acyltransferase, diacylglycerol cholinephosphotransferase and diacylglycerol ethanolaminephosphotransferase) are hormonally regulated and how these microsomal enzymes of triacylglycerol and phospholipid synthesis are altered during the differentiation of "pre-adipocytes" to "adipocytes" in culture. Preliminary experiments on the hormonal regulation of the sn-glycerol-3-phosphate acyltransferase have resulted in the discovery of a soluble factor which inactivated the acyltransferase in vitro. Experiments on the purification, characterization, and physiological significance of this factor are proposed as well as the solubilization purification, and characterization of the acyltransferase. The sn-glycerol-3-phosphate and dihydroxyacetone phosphate acyltransferase activities of liver microsomes will be investigated to see if a single microsomal enzyme catalyzes both reactions and for comparison with the activities from isolated fat cells. Preliminary data raises the question of the existence of microsomal isoenzymes. The proposed experiments promise novel significant data about the enzymes of phospholipid and triacylglycerol synthesis from adipocytes and how they are regulated.